Spectrophotometers are useful in many detection regimes as they can effectively measure the result of light-matter interaction at multiple wavelengths. The interaction can take the form of absorbance as light is transmitted through a sample, changes to the light as it is scattered from a sample, or emission of light as a result of an interaction. By measuring a response at multiple wavelengths, spectrophotometers can acquire a great deal of information that can be used to distinguish various sources of signal changes, e.g., multiple analytes. These capabilities allow the spectrophotometer to be used in situations where the properties of the sample may be changing over time, e.g. as a monitor for a particular analyte in a chemical process. As a result of such capabilities the accuracy of analyte detection and measurement with spectrophotometers can be higher than with other detection approaches.
Unfortunately, spectral analysis is limited to a single snapshot of a sample or event at the particular time of detection. For instance, in order to monitor an analyte in a chemical process, a plurality of samples will generally be collected over the time period of interest, with each sample then separately analyzed. While such a single-shot approach is highly effective in many situations, it will not work for temporal examination of a high speed event. For example, during laser-induced breakdown spectroscopy (LIBS), a laser is focused to form a plasma that is then used to ablate and excite a sample. LIBS is often used to evaluate the presence or abundance of constituent elements in a sample, but in practice, detection is limited to a very small light collection window and as such a temporally gated detector is utilized. If this window is mistimed the results of the detection protocol can be inaccurate. Moreover, a laser-induced plasma can emit a continuum of radiation over a time period on the order of microseconds or milliseconds, and the spectral analysis capability of current systems cannot provide information with regard to changes in the spectral activity of the system over the course of the entire time period. Use of time gated detectors has provided one route for temporal characterization, but this approach calls for repetition of an experiment with each repetition using a set of different time gates. Unfortunately however, some events cannot be easily repeated.
Another example of a transitory system for which high speed temporal spectroscopy would be useful is in the study of detonation of high energy devices in which the temporal formation of particulates and the correlation with radiant emissions are not well understood. Spectral emission from elemental and molecular species during high energy device detonations (or simulations thereof) can be used to better understand the activities and changes of materials under high temperatures and pressures. Since spectral information is highly dependent on temporal behavior over the course of such a high speed event, it would be highly beneficial to investigate the variation of spectra on the temporal scale of a detonation.
What are needed in the art are optical measurement systems and methodologies that can be used to examine a system over the course of a high speed event, for instance an event measured on the order of milliseconds or less.